Star Formation and Protostars at High Angular Resolution with the SMA

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Star Formation and Protostars at High Angular
Resolution with the SMA

• Jes Jørgensen (CfA)Tyler Bourke, Philip Myers,
  David Wilner (CfA), Fredrik Schöier (Stockholm),
  Ewine van Dishoeck (Leiden), ... and the PROSAC
  team.

ACP
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Dark Cloud Cores
t 0Gravitational collapse
t 104 105 yrs Protostar embedded in 10,000
AU envelope
Figure based on Shu (1987) from NASA Origins
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Low-mass protostars
20,000 AU (100)
200 AU (1)

• Densities ranging from 104 cm-3 to 107-108 cm-3
  (H2)
• Temperatures ranging from 10 K to a few hundred
  K.

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PROSAC
PROtostellar Submillimeter Array Campaign
Jørgensen (PI)Bourke, Di Francesco, Lee, Myers,
Ohashi,Schöier, Takakuwa, van Dishoeck, Wilner,
Zhang

• Line continuum survey (230/345 GHz) of deeply
  embedded (class 0) protostars
• 8 protostellar sources from Ph.D. thesis of J.
  Jørgensen (Leiden Univ. 2004 Jørgensen et al.
  2002, 2004, 2005)...
• Single-dish survey at JCMT and Onsala 20m
  telescopes.
• Follow-up 1, 3 mm interferometric measurements
  OVRO and BIMA.
• All tied together by detailed line and continuum
  rad. transfer models.
• 3 spectral setups per source CO, CS, SO, HCO,
  H2CO, CH3OH, SiO, ... transitions (and isotopes)

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In this talk...

• What is the structure of protostellar envelopes
  on a few 100 AU scales?
• What is the physical structure of circumstellar
  disks - and their molecular content?
• Do low-mass protostars have hot cores, i.e.,
  inner regions with temperatures higher than 100 K
  and where complex organic molecules might be
  present?

Jørgensen et al., ApJ, submitted
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NGC1333-IRAS2
SCUBA 850 µm

• Tbol 50 K, Lbol 16 L?
• d 220 pc (Cernis, 1990)

• Three pre/protostellar objects (Looney et al.
  2000, Sandell Knee 2001, Jørgensen et al. 2004)

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NGC1333-IRAS2A dust continuum at 850 µm.
SMA 850 µm
SCUBA 850 µm
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NGC1333-IRAS2A dust continuum at 850 µm.
the SMA resolves the warm dust in the inner
envelope and the circumstellar disk
SMA 850 µm
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NGC1333-IRAS2A dust continuum at 850 µm.

• The dust continuum emission follows a power-law F
  ? ? 2.2 from cm through submillimeter
  wavelengths.
• Likely optically thick thermal dust emission from
  a circumstellar disk with a size of 300 AU and
  mass of a few ? 0.01-0.1 M?
• It is not evident from high-resolution data that
  the envelope extends all the way to the smallest
  scales.
• The disk material will be dominating a hot core
  in the protostellar envelope.

cm through mm measurements from Rodríguez et al.
(1999), Reipurth et al. (2002), Jørgensen et al.
(2004)
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Envelope and disk chemistry

• Low-mass hot cores Presence of complex organic
  species on small scales (i.p., IRAS16293 Kuan et
  al. (2004), Bottinelli et al. (2004)).

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Detections of high excitation transitions of CO,
HCN (and H13CN), SO, SO2, CH3OH (and CH3OD),
CH3OCH3 and CH3OCHO (tentative) in submm window
toward NGC1333-IRAS2A.
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Organic molecules toward IRAS2A
...line emission compact (largely unresolved)
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Envelope and disk chemistry

• Low-mass hot cores Presence of complex organic
  species on small scales (i.p., IRAS16293 Kuan et
  al. (2004), Bottinelli et al. (2004)).
• Complex organic species detected on small scales
  in IRAS2A.
• ...but in the 2 SMA beam the disk column
  density is dominating compared to the hot core.
• Sulfur species are expected to be enhanced in
  typical hot cores (Charnley 1997, Wakelam et al.
  2004)

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Envelope and disk chemistry
Constant abund. envelope
The SO abundance is almost constant throughout
the envelope (consistent with single-dish obs. of
S-species). An abundance enhancement in the
innermost envelope is clearly ruled out.
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Envelope and disk chemistry

• Low-mass hot cores Presence of complex organic
  species on small scales (i.p., IRAS16293 Kuan et
  al. (2004), Bottinelli et al. (2004)).
• Complex organic species detected on small scales
  in IRAS2A.
• ...but in the 2 SMA beam the disk column
  density is dominating compared to the hot core.
• Sulfur species are expected to be enhanced in
  typical hot cores (Charnley 1997, Wakelam et al.
  2004), but are not in IRAS2A.
• The presence of the high excitation lines of in
  particular CH3OH suggests that the temperature is
  high 150 K. Heated layer of circumstellar disk
  (e.g., Elias 29 Ceccarelli et al. 2002)?

Jørgensen et al., ApJ, submitted
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PROSAC Protostellar Submillimeter Array
Campaign
...much more to come!
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Conclusions

• High-angular resolution interferometric and
  single-dish continuum observations of NGC
  1333-IRAS2A can be fitted by an extended envelope
  and a 300 AU (resolved) disk with a mass a few ?
  0.01-0.1 M?.
• The large size of the disk suggests a rapid
  build-up of disks in the deeply embedded stages
  of protostellar evolution.
• The molecular content of the disk is
  non-negligible compared to a candidate hot core.
  It is not evident from the dust
  observations/models that warm (T gt 100 K)
  material is present in the envelope around
  NGC1333-IRAS2A.
• No evidence is seen for sulfur enhancements on
  small-scales. Other species such as CH3OH may
  have their origin in the circumstellar disk...
  (dont forget the outflows, though)